A novel and useful mm-wave frequency generation system is disclosed that takes advantage of injection locking techniques to generate an output oscillator signal with improved phase noise (PN) performance and power efficiency. Low frequency and high frequency DCOs as well as a pulse generator make up the oscillator system. A fundamental low frequency (e.g., 30 GHz) signal and its sufficiently strong higher (e.g., fifth) harmonic (e.g., 150 GHz) are generated simultaneously in a single oscillator system. The second high frequency DCO having normally poor phase noise is injected locked to the first low frequency DCO having good phase noise. Due to injection locking, the high frequency output signal generated by the second DCO exhibits good phase noise since the phase noise of the second DCO tracks that of the first DCO.
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13. A method of generating an output oscillator signal, comprising:
generating a reference frequency signal containing a plurality of millimeter wave harmonics;
first injection locking a first oscillator to one of the plurality of millimeter wave harmonics thereby generating a millimeter wave fundamental first oscillator signal and a harmonic thereof, said first oscillator operative to resonate at a frequency of said fundamental first oscillator signal; and
second injection locking a second oscillator to the harmonic output of said first oscillator and generating the output oscillator signal therefrom at an output node, said second oscillator operative to resonate at a frequency of said harmonic output of said first oscillator.
1. An oscillator system, comprising:
a reference frequency pulse generator operative to generate a reference signal containing a plurality of harmonics;
a first oscillator operative to receive said reference signal output by said pulse generator and to resonate at and generate a first fundamental frequency and one or more harmonic signals therefrom, wherein said first oscillator is injection locked to said pulse generator at one of said plurality of harmonics generated by said pulse generator; and
a second oscillator operative to receive and resonate at said one of the harmonic signals output by said first oscillator, and to generate an output signal therefrom at a frequency of the one of the harmonic signals output by said first oscillator, wherein said second oscillator is injection locked to said first oscillator at the frequency of the one of the harmonic signals output from said first oscillator.
7. An oscillator system, comprising:
a pulse generator having relatively good phase noise operative to generate a reference frequency signal containing a plurality of harmonics;
a first oscillator operative to receive said reference frequency signal and to resonate at and generate a millimeter wave output fundamental frequency signal and a higher harmonic signal, wherein said first oscillator is injection locked to said reference frequency signal output of said pulse generator at one of the plurality of harmonics generated by the pulse generator; and
a second oscillator having relatively poor phase noise operative to receive the higher harmonic signal, and to generate an output oscillator signal therefrom at a frequency of the higher harmonic signal and at an output node having relatively good phase noise, wherein said second oscillator is injection locked to said first oscillator at the frequency of the higher harmonic signal, wherein the phase noise of said second oscillator tracks that of said first oscillator.
18. An oscillator system, comprising:
a pulse generator having relatively good phase noise operative to generate a reference frequency signal having a plurality of harmonics;
a first oscillator operative to receive the reference frequency signal output by said pulse generator and to resonate at and generate a fundamental signal and to also generate a first higher harmonic signal therefrom, wherein said first oscillator is injection locked to a first one of the plurality of harmonics output of said pulse generator;
a second oscillator operative to receive said first higher harmonic signal, to resonate at said first higher harmonic signal, to generate a first output oscillator signal at an output node at a frequency of said first higher harmonic signal, wherein said second oscillator is injection locked to said first oscillator at the frequency of said first higher harmonic signal causing the phase noise of said second oscillator to track that of said first oscillator; and
a third oscillator operative to receive said reference signal and to generate a second output signal therefrom at a second higher harmonic frequency, wherein said third oscillator resonating at and injection locked to a second one of the plurality of harmonics output of said pulse generator, wherein the phase noise of said third oscillator tracks the relatively good phase noise of said pulse generator.
2. The oscillator system according to
3. The oscillator system according to
4. The oscillator system according to
5. The oscillator system according to
6. The oscillator system according to
8. The oscillator system according to
9. The oscillator system according to
10. The oscillator system according to
11. The oscillator system according to
12. The oscillator system according to
14. The method according to
15. The method according to
16. The method according to
17. The method according to
19. The oscillator system according to
20. The oscillator system according to
said second higher harmonic output of said pulse generator comprises a fifth harmonic thereof.
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This application claims priority to U.S. Provisional Application Ser. No. 62/621,611, filed Jan. 25, 2018, entitled “Multi-Stage Sub-THz Frequency Generator Using Injection Locking,” incorporated herein by reference in its entirety.
The present invention relates to the field of semiconductor integrated circuits and more particularly relates to a multi-stage sub-THz frequency generator that utilizes injection locking techniques.
High frequency oscillators are the key blocks in mm-wave front-end circuits which are mainly focusing on short-range high-speed links (e.g., IEEE 802.1 lad/y, mm-wave 5G), FMCW automotive radars (e.g., 76-81 GHz), and imaging and security applications above 100 GHz. Currently, many high frequency oscillators are typically implemented in silicon/germanium (SiGe) technology due to wider RF passive devices support, higher speeds over earlier CMOS nodes, and potential baseband integration through BiCMOS extensions which are more expensive compared to CMOS technology. On the other hand, designing high speed oscillators in CMOS technology is much more challenging since the quality factor of passive components are lower than other technology.
There is thus a need for a high frequency oscillator that does not suffer from the disadvantages of the prior art. The oscillator should have improved phase noise and power efficiency and not require use of a buffer or amplifier at the output.
A novel and useful mm-wave frequency generation system is disclosed that takes advantage of injection locking techniques to generate an output oscillator signal with improved phase noise (PN) performance and power efficiency. A fundamental low frequency (e.g., ˜30 GHz K-band) signal and its sufficiently strong higher (e.g., fifth) harmonic at a high frequency (e.g., ˜150 GHz D-band) are generated simultaneously in a single oscillator.
Several features and advantages of the oscillator architecture of the present invention includes: (1) injecting pulse generator harmonics to a first oscillator; (2) injecting the higher (e.g., fifth) harmonic to a second oscillator; (3) generating higher (e.g., fifth) harmonics in class F; (4) injecting the higher (e.g., fifth) harmonic of class F to a second oscillator rather than extract it; and (5) not requiring a buffer and delivering maximum power at a relatively high frequency and without the need for a power hungry power amplifier.
Note that the oscillator architecture of the present invention has been implemented in 28 nm CMOS technology. Using the circuit structure described herein, the total power consumption of the system is approximately 40 mW while it delivers 1.7 dBm output power at 150 GHz. As a result, a very low phase noise oscillator with high power efficiency can be achieved using CMOS technology.
The oscillator system described herein is suitable for automotive radar, phased array, imaging, and security applications since it exhibits very good phase noise and output power. Moreover, since it provides relatively high output power at 150 GHz with tight coupling to the 30 GHz stage, it can be directly connected to an antenna and function as a power amplifier. In addition, due to its low power consumption, the oscillator system can be used in systems which need to save power.
There is thus provided in accordance with the invention, an oscillator system, comprising a reference frequency pulse generator operative to generate a reference signal containing a plurality of harmonics, a first oscillator operative to receive said reference signal output by said pulse generator and to generate a first fundamental frequency and one or more harmonic signals therefrom, wherein said first oscillator is injection locked to said pulse generator, and a second oscillator operative to receive one of the harmonic signals output by said first oscillator, and to generate an output signal therefrom, wherein said second oscillator is injection locked to said first oscillator.
There is also provided in accordance with the invention, an oscillator system, comprising a pulse generator having relatively good phase noise operative to generate a reference frequency signal containing a plurality of harmonics, a first oscillator operative to generate a millimeter wave output fundamental signal along with a higher harmonic signal, wherein said first oscillator is injection locked to said reference frequency signal output of said pulse generator, and a second oscillator normally having relatively poor phase noise operative to generate an output oscillator signal at an output node having relatively good phase noise, wherein said second oscillator is injection locked to said first oscillator causing the phase noise of said second oscillator to track that of said first oscillator.
There is further provided in accordance with the invention, a method of generating an oscillator signal, comprising generating a reference frequency signal, first injection locking a first oscillator and to the reference frequency signal thereby generating a millimeter wave first oscillator signal along with a harmonic signal, wherein phase noise of said first oscillator tracks that of said reference frequency signal, and second injection locking a second oscillator to the harmonic signal and generating an output oscillator signal therefrom at an output node, and wherein the phase noise of said second oscillator tracks that of said first oscillator.
There is also provided in accordance with the invention, an oscillator system, comprising a pulse generator having relatively good phase noise operative to generate a reference frequency signal having a plurality of harmonics, a first oscillator operative to receive the reference frequency signal and to generate a fundamental signal along with a higher harmonic signal therefrom, wherein said first oscillator is injection locked to the reference frequency signal output of said pulse generator, a second oscillator normally operative to generate a first output oscillator signal at an output node, wherein said second oscillator is injection locked to said first oscillator causing the phase noise of said second oscillator to track that of said first oscillator, and a third oscillator operative to generate a second output signal, wherein said third oscillator indirectly injection locked to said reference frequency signal output of said pulse generator causing the phase noise of said third oscillator to track that of said pulse generator.
The present invention is explained in further detail in the following exemplary embodiments and with reference to the figures, where identical or similar elements may be partly indicated by the same or similar reference numerals, and the features of various exemplary embodiments being combinable. The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein:
The present invention is a novel and useful mm-wave frequency generation system that takes advantage of injection locking techniques to generate an output oscillator signal with improved phase noise (PN) performance and power efficiency. A fundamental low frequency (e.g., 30 GHz) signal and its sufficiently strong higher (e.g., fifth) harmonic at a high frequency (e.g., 150 GHz) are generated simultaneously in a single oscillator.
A high-level block diagram illustrating an example high frequency oscillator employing a multiplier technique is shown in
A high-level block diagram illustrating an example high frequency oscillator employing a push-push technique is shown in
An oscillator with m-push oscillators utilize frequency dividers operating at 150/m GHz, avoiding the use of frequency multipliers. This oscillator type, however, suffers from low output power and mismatches among the m oscillators. Among this type, push-push oscillators are the most common and easiest to implement. The required large common mode (CM) swing, however, can increase the 1/f noise upconversion. Moreover, the conversion from single-ended CM signal to a differential output may introduce large phase error.
Both of these oscillator circuits, suffer from high power consumption and low output power. Thus, the power efficiency of these oscillator circuit techniques is a significant bottleneck to using them in real world applications.
A high-level block diagram illustrating an example fundamental high frequency oscillator is shown in
Several difficulties of designing oscillators of the type described supra include (1) the parasitic capacitance of active devices takes up a large share of the relatively small tank capacitance, thus limiting the frequency tuning range; (2) to achieve a tuning range of >15%, the poor Q-factor of the tuning capacitance dominates the Q-factor of the resonator, thus limiting the achievable phase noise. The 150 GHz frequency dividers must achieve large locking range to ensure sufficient overlap with the oscillator tuning range under PVT variations. There is a strong tradeoff, however, between the locking range and the power consumption.
To alleviate the design challenges for mm-wave oscillators and dividers without shifting more stress onto other blocks, a 150 GHz frequency generation technique based on a 30 GHz oscillator and higher (e.g., fifth) harmonic is disclosed. To realize that goal, the higher (e.g., fifth) harmonic as well as the fundamental are applied to a 30 GHz transformer-based dual-resonance oscillator. Using this technique, the higher (e.g., fifth) harmonic is the signal of interest.
In accordance with the invention, both a low frequency fundamental (e.g., 30 GHz) and a significant level of its higher (e.g., fifth) harmonic at a high frequency (e.g., 150 GHz) are simultaneously generated within a low frequency, e.g., 30 GHz, oscillator. The generated 150 GHz signal is fed to a second high frequency oscillator. Since, in one embodiment, the oscillator runs at the fundamental frequency of 30 GHz, its resonant tank achieves a better Q-factor than at 150 GHz, which leads to better PN performance. Moreover, the tank has a larger inductance and capacitance. This increases the variable portion of the total tank capacitance and the frequency tuning range.
A high-level block diagram illustrating an example multi-stage high-frequency oscillator utilizing injection locking techniques is shown in
In this example embodiment, the oscillator architecture is based on an injection locking technique. The pulse generator 42 functions as a reference frequency. This eases the design of the frequency divider when the oscillator 40 is used to implement a phase locked loop (PLL). The pulse generator is operative to generate one or more harmonics (n harmonics in this example). The low frequency DCO 44 is injection locked to one of the harmonics generated by the pulse generator. In this example embodiment, the pulse generator fundamental period is 60 ps which corresponds to approximately 16 GHz. The second harmonic at 32 GHz is injection locked to the first low frequency DCO.
In one embodiment, the first DCO comprises a 30 GHz oscillator such as a class F oscillator adapted to produce relatively strong 5th harmonics at 150 GHz. Since the first oscillator is injection locked to the pulse generator which is designed to exhibit relative very good phase noise, the first oscillator output signal (i.e. fundamental as well as harmonics) also has relatively very clean phase noise as well.
The second DCO comprises a relatively high frequency oscillator circuit. In one example, the second oscillator is adapted to generate a 150 GHz signal. The second DCO, however, is designed to normally exhibit relatively poor phase noise performance, i.e. when the DCO is stand-alone without any injection locking in order to conserve power. The signal output of the class F oscillator (i.e. first DCO) is injection locked to the second oscillator which normally features poor phase noise. Note that the strong 5th harmonic of the first oscillator can be injected simultaneously with the fundamental frequency (e.g., 30 GHz) signal to the second oscillator stage, i.e. the high frequency oscillator which in this example embodiment is 150 GHz. This causes the second 150 GHz oscillator to lock relatively easily to the first 30 GHz oscillator. Consequently, the second high frequency oscillator tracks the phase noise of the first oscillator within a relatively wide locking range.
Thus, using this injection locking technique relaxes the design challenges of the second oscillator at 150 GHz at least from a phase noise point of view. Since the injection signal generated by the first oscillator is strong, the second oscillator having wide locking range is locked to the first oscillator and tracks its phase noise. Moreover, since the second oscillator (e.g., 150 GHz) is used as the output stage instead of a multiplier in the architecture described supra, it provides relatively high output voltage swing and high output power at 150 GHz while consuming less power.
A schematic diagram illustrating the circuit implementation of an example multi-stage high-frequency oscillator utilizing injection locking techniques is shown in
The class F low frequency oscillator 56 comprise transistors M1 and M2 and is adapted to produce relatively strong 5th harmonics. Using the injection transistors Minj, the 5th harmonics of the low frequency oscillator 56 is injected to the second stage high frequency oscillator 58 via transistors M3 and M4 which in one example embodiment comprises a 150 GHz oscillator normally having relatively poor phase noise. At the output stage, in order to separate the output node from pad parasitics and also deliver maximum power to output, transformer 59 with coupling factor km2 is used. Note that a load-pull simulation has been performed at the output stage to determine the required impedance which provides both oscillation and delivers maximum power to the output node.
The class F low frequency oscillator 56 comprise transistors Mi and M2 and is adapted to produce relatively strong 5th harmonics. Using the injection transistors Minj, the 5th harmonics of the low frequency oscillator 56 is injected to the second stage high frequency oscillator 58 via transistors M3 and M4 which in one example embodiment comprises a 150 GHz oscillator normally having relatively poor phase noise. At the output stage, in order to separate the output node from pad parasitics and also deliver maximum power to the output, transformer 59 with coupling factor km2 is used. Note that a load-pull simulation has been performed at the output stage to determine the required impedance which provides both oscillation and delivers maximum power to the output node.
In one embodiment, the L and C ratios in primary and secondary windings of the transformer based dual tank resonator were optimized to realize fundamental oscillation and its higher (e.g., fifth) harmonic resonance.
A schematic diagram illustrating an example pulse generator is shown in
In the example embodiment shown, the noise-free pulse generator comprises a crystal oscillator (XO) slicer that combines the programmable edge delay. The voltage offset ΔV gets converted to time offset ΔT (by adding extra offset-inducing transistors) by delaying the threshold detection of the sinusoidal waveform. This mechanism does not appreciably add any extra noise. Note that the pulse width is controlled from 10-30 ps (or 55-70 ps) with a multibit code.
A schematic diagram illustrating an example multi-stage dual high-frequency oscillator utilizing injection locking techniques is shown in
The third 79 GHz oscillator 78 is used in a second path which is locked directly to the pulse generator 72. In this embodiment, the first path is the same as the oscillator shown in
A schematic diagram illustrating an example transformer circuit is shown in
A diagram illustrating X-factor versus harmonic ratio for different values of km is shown in
Trace 100 represents the harmonic ratio for km=0.9; trace 102 represents the harmonic ratio for km=0.8; and trace 104 represents the harmonic ratio for km=0.7.
A diagram illustrating the dependency of X-factor on km when
is shown in
A diagram illustrating the dependency of tank input resistance on km is shown in
In one embodiment, as a trade-off between a large higher (e.g., fifth) harmonic and optimal oscillator performance, km=0.67 is selected for Rp5/Rp1=2 with sufficient Q. A diagram illustrating the dependency of the normalized resonance frequency on km is shown in
Intuitively, we know that the drain current of oscillator in the presence of harmonics is close to a square wave as shown in
According to Equation 2, the higher (e.g., fifth) harmonic is a very weak signal. Thus, having passive gain helps to inject a stronger higher (e.g., fifth) harmonic signal to the high frequency (e.g., 150 GHz) oscillator which improves the locking range of the oscillator system. This provide additional motivation to select a coupling factor of km=0.67.
A diagram illustrating an example ratio of fifth harmonic to fundamental magnitude is shown in
A diagram illustrating the transformed-based tank input impedance Z11 magnitude is shown in
A diagram illustrating simulated open loop response of the transformed-based tank trans-impedance Z21 magnitude is shown in
where km, Lp, Ls, C1, C2, rp, and rs are the magnetic coupling factor of the transformer, primary and secondary inductance, tuning capacitor on the primary and secondary side, and model the equivalent series resistance of the primary and secondary inductance, respectively. In order to find the poles of this transfer function, the equation is solved for the denominator=0 which yields
Since we are interested in the higher (e.g., fifth) harmonic, the ratio
as a result is given by
where
By solving Equation 5, we obtain X as a function of km, as shown in
To determine Rp1 and Rp5, the real part of Equation 3 must be determined first as follows
where A, B, C, D, and E are calculated as follows
A=C2(Lsrp+Lprs)
B=LpLsC2(1−km2)
C=LpC1+LsC2+rprsC1C2
D=(Lp+rsrpC2)
E=(rpC1+r8C2) (7)
Rp1 and Rp5 are calculated as Rp1={Zin(ω1}, Rp5={Zin(ω2} where it is known that ω2=5ω1. The results are shown in
The transimpedance of the tank from primary to secondary winding is as follows
where the equivalent quality factor is derived from the phase response of the open-loop transfer function of −GmZ21(jω)
where Qp and Qs are the quality factor of the primary and secondary winding, respectively. Since the phase noise response is defined by the equivalent quality factor on the primary side. Note that Equation 9 has been plotted for the fundamental frequency f0=30 GHz and as shown in
Several transformer characteristics are shown in
A diagram illustrating the oscillator voltage waveform in differential mode is shown in
A diagram illustrating the oscillator gate voltage waveform is shown in
A diagram illustrating example phase noise of the oscillator circuit of
A diagram illustrating a first example locked signal spectrum of the oscillators is shown in
Those skilled in the art will recognize that the boundaries between logic and task blocks are merely illustrative and that alternative embodiments may merge logic or task blocks or impose an alternate decomposition of functionality upon various logic or task blocks. Thus, it is to be understood that the architectures depicted herein are merely exemplary, and that in fact many other architectures may be implemented which achieve the same functionality.
Any arrangement of components to achieve the same functionality is effectively “associated” such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality may be seen as “associated with” each other such that the desired functionality is achieved, irrespective of architectures or intermediary components. Likewise, any two components so associated can also be viewed as being “operably connected,” or “operably coupled,” to each other to achieve the desired functionality.
Furthermore, those skilled in the art will recognize that boundaries between the above described operations merely illustrative. The multiple operations may be combined into a single operation, a single operation may be distributed in additional operations and operations may be executed at least partially overlapping in time. Moreover, alternative embodiments may include multiple instances of a particular operation, and the order of operations may be altered in various other embodiments.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The use of introductory phrases such as “at least one” and “one or more” in the claims should not be construed to imply that the introduction of another claim element by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim element to inventions containing only one such element, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an.” The same holds true for the use of definite articles. Unless stated otherwise, terms such as “first,” “second,” etc. are used to arbitrarily distinguish between the elements such terms describe. Thus, these terms are not necessarily intended to indicate temporal or other prioritization of such elements. The mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to advantage.
The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. As numerous modifications and changes will readily occur to those skilled in the art, it is intended that the invention not be limited to the limited number of embodiments described herein. Accordingly, it will be appreciated that all suitable variations, modifications and equivalents may be resorted to, falling within the spirit and scope of the present invention. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.
Staszewski, Robert Bogdan, Bozorg, Amirhossein Ansari
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